Non-Patent Document 1 discloses a homologous series represented by In1−xGa1+xO3(ZnO)m (−1≦x≦1, and m is a natural number). Furthermore, Non-Patent Document 1 discloses a solid solution range of the homologous series. For example, in the solid solution range of the homologous series in the case where m is 1, x ranges from −0.33 to 0.08, and in the solid solution range of the homologous series in the case where m is 2, x ranges from −0.68 to 0.32.
Furthermore, a technique for forming a transistor using an In—Ga—Zn-based oxide semiconductor is disclosed (see, for example, Patent Document 1).